Cathode-ray tube with parallel slit grid structure adjacent color display screen

ABSTRACT

A color picture tube or other cathode-ray tubes in which a plurality of electron beams emanating from one or more cathodes are made to converge substantially at the optical center of an electrostatic focusing lens which focuses the beams on an electron receiving screen. When beams are focused on the electron receiving screen are all to converge at a common point on such screen an electrostatic or magnetic deflection device acts on those beams which diverge after passing through the lenslike focusing system. A grid is positioned adjacent the electron receiving screen of the tube in order to sharply focus the electron beams on the electron receiving screen. The support for the grid structure is stressed to compensate for any expansion of the grid wires due to heating. The support has a pair of opposed parallel arms with the grid wires attached to and extending transversely between the arms and a pair of braces supporting the arms at the bessel point, the braces being stressed in a direction substantially parallel to the direction of the grid wires so that as the grid wires expand due to heat, the braces will expand a corresponding amount to maintain a substantially constant tension on the grid wires.

United States Patent [72] inventors Susulnu Yoahida;

Aldo Ohgoshl, Tokyo; Senrl Miyanlta, Kanagawa-lten; Yoshlllaru Katagiri,Tokyo, all of, Japan [21] Appl. No. 829,295

[22] Filed June 2, 1969 [45] Patented July 27, 1971 [73] Assignee SonyCorporation Tokyo, Japan [32] Priority Jan. 14, 1967, Mar. 22, 1967 [3142/2629 and 42/ 17856 Continuation-impart of application Ser. No.697,414, Jan. 12, 1968, now Patent No. 3,448,316, dated June 3, 1969.

[54] CATHODE-RAY TUBE WITH PARALLEL SLl'l GRID STRUCTURE ADJACENT COLORDISPLAY SCREEN 2 Claims, 3 Drawing Figs.

[52] U.S.Cl 313/86,

[51] int. Cl '.1401) 29/56,

i-iOij 29/80, HOIj 29/06 [50] Field of Search 313/92 PD, 85,69 C, 70 C,92 8, 86

[56] References Cited UNITED STATES PATENTS 2,777,088 1/1957 Laffcrty313/92 PDF X 2,832,911 4/1659 Van Velzer............ 313/ 85 x 2,862,10711/1958 Cummings.................... 3| 3/85 X 3,462,638 8/1969 Tetsuoet al. 313/70 C X FOREIGN PATENTS 1,071,963 6/1967 Great Britain 313/85Primary Examiner-Robert Segal Attorneys-Albert C. Johnston, Robert E.lsner, Lewis H.

Ealinger and Alvin Sinderbrand ABSTRACT: A color picture tube or othercathode-ray tubes in which a plurality of electron beams emanating fromone or more cathodes are made to converge substantially at the opticalcenter of an electrostatic focusing lens which focuses the beams on anelectron receiving screen. When beams are focused on the electronreceiving screen are all to converge at a common point on such screen anelectrostatic or magnetic deflection device acts on those beams whichdiverge after passing through the lenslike focusing system. A grid ispositioned adjacent the electron receiving screen of the tube in orderto sharply focus the electron beams on the electron receiving screen.The support for the grid structure is stressed to compensate for anyexpansion of the grid wires due to heat ing. The support has a pair ofopposed parallel arms with the grid wires attached to and extendingtransversely between the arms and a pair of braces supporting the armsat the bessel point, the braces being stressed in a directionsubstantially parallel to the direction of the grid wires so that as thegrid wires expand due to heat, the braces will expand a correspondingamount to maintain a substantially constant tension on the grid wires.

PATENTEU JULZT IBYI 4 mv- TORS SUSUMU YOSHIDA AKIO OHGOSHI SENR! MIYAOKAVOSHIHARU KATAGIRI iwe CATHODE-RAY TUBE WI'I'II PARALLEL SLI'I GRIDSTRUCTURE ADJACENT COLOR DISPLAY SCREEN This application is acontinuation-in-part application of our copending application Ser. No.697,414, filed Jan. 12, 1968 and issuing June 3,1969 as US. Pat. No.3,448,3 I 6.

This invention generally relates to cathode-ray tubes and isparticularly directed to improvements in color cathode-ray tubes of thetype in which a single electron gun is provided for emitting a pluralityof electron beams in order to produce a color picture such for exampleas in color television receivers.

Existing color picture tubes are usually of the multigun type andinclude three independent electron guns emitting respective electronbeams which are modulated by corresponding color signals and acted uponby a grid system so as to be focused on a collector or electronreceiving screen which may be simply a phosphor or luminescence screenor a phosphorus screen with a perforated electrode or shadow mask infront thereof. The three electron guns have to be aligned with respectto each other so that the emitted electron beams converge at theelectron receiving screen. Such color picture tubes of the multigun typeare disadvantageous in that it is difficult to obtain and maintain theprecise alignment of the three electron guns required for theconvergence of their beams on the electron receiving screen and anymisconvergence of the beams causes deterioration of the quality andresolution of the color picture that results.

In an attempt to avoid the above-mentioned disadvantages and limitationsof the existing color picture tubes of the multigun type, it has beenproposed to provide a color picture tube of the single gun plural beamtype in which a single electron gun emits three beams from either threerespective cathodes or a single cathode and the three electron beams arepassed through a lenslike focusing system so as to converge at theelectron receiving screen. However, in the tubes of the single gunplural beam type heretofore proposed. no more than one of the electronbeams passes through the lenslike focusing system at the optical axis ofthe latter and the beams that pass through the focusing system at adistance from the optical axis are subject to coma and sphericalaberration. By reason of such coma and spherical aberration and theconsequent deterioration of the quality of the color picture thatresults, color picture tubes of the single gun plural beam type have notenjoyed any widespread use.

In my copending patent application filed Jan. I2, 1968, and bearing U.S.Pat. No. 3,448,3l6 entitled CATHODE-RAY TUBE, there is described acathode-ray tube adapted for use in a color television receiver andwhich is provided with a single electron gun. This gun includes acathode structure that emits electrons which are formed into a pluralityof electron beams and such beams are made to converge substantially atthe optical center of a lenslike electrostatic focusing lens which iscommon to all the beams and focuses the beams on the electron receivingscreen whereby the introduction of spherical aberration is diminished.

In cases where the electron beams are emitted parallel to each other,the convergence of the beams at the optical center of the lenslikefocusing means is effected by an auxiliary electrostatic lens locatedbetween the grid structure which forms the electron beams and thefocusing lens. When it is desired that the beams focused on the electronreceiving screen be converged at a common point on the screen the beamswhich diverge from the focusing lens are acted upon by eitherelectrostatic or magnetic deflection means located between the focusinglens and the screen.

As is well known in the prior art, color cathode-ray tubes employ, forelectron beam postdeflection and focusing, a grid structure such that aplurality of parallel grid wires are stretched across a parallelograrnicframe between a pair of opposed sides. Such a grid structure is producedin the following manner. A plurality of parallel grid wires arestretched on a master frame under predetermined taut conditions and agrid frame is put on the grid wires from inside of the master frame.

The grid wires are then fixed to a pair of opposed supports of the gridframe and are thereafter severed along the margins of the grid frame. Inthis case, the grid frame is prcstressed inwardly by a turnbuckle toapply a maximum tension to the grid wires secured to the central portionof the opposed supports of the grid frame and a smaller tension to thosefixed to end portions of the supports, ensuring that all the grid wiresare subjected to substantially uniform tension by the restoring force ofthe prcstressed grid frame after disassembling it from the master frame.

Such a grid structure may be regarded as one where a plurality of gridwires are stretched at substantially uniform ten sion on aparallelogramic frame prcstressed in a manner to be displaced the mostat the center of the frame. When a predetermined positive potential isapplied to such a grid structure and electron beams are emitted from theelectron gun of a cathode-ray tube toward the fluorescent screenthereof, electron beams of several to lO-odd percent strike against thegrid wires and are discharged therethrough to thereby heat the gridwires. As a result of this, the temperature of the grid wires is raisedseveral-l0" and the wires expand. An examination of the expanded gridwires shows that since the displacement of the frame is greatest at thecenter thereof, elongation of the grid wires of that portion due to thethermal expansion is cancelled by the restoring force of the prcstressedframe as if the grid wires had not been elongated. Accordingly, the gridwires are still subjected to substantially the same original tension,and hence do not sag. The elongation of the grid wires lying on bothsides of the central grid wires cannot be absorbed with the displacementof the frame at those particular portions, since the displacement isbasically small. Consequently, when the elongation of the grid wiresexceeds the displacement of the frame, the grid wires are likely to sag.Even if the grid wires do not sag, they are not pulled at apredetermined tension and are readily vibrated at great amplitude tolower the picture quality of the reproduced picture when subjected toaccidental small shocks.

The above can be easily understood from the fact that when all the gridwires have substantially the same length, the amount of restoration ofthe frame on both sides of the center thereof is smaller than that ofthe central portion.

This defect is remarkable especially in the grid structure of a colorcathode-ray tube of the type where a plurality of ribbonlike gridelements are stretched in parallel with phosphor strips and function asa kind of shadow mask. In this type of structure three electron beamsare impinged upon three different color emissive phosphor strips throughslits defined between adjacent grid elements.

A grid structure such as described above has been proposed in an attemptto increase the electron beam transmission factor of the so-calledshadow mask in which a plate having bored therethrough a plurality ofapertures is used as a mask for the electron beam. In such a gridstructure, however, the grid elements are secured only at both ends tothe frame, so that the grid elements heated by electron beams strikingthereon radiate heat mainly through the ends fixed to the frame.Further, the transmission factor of the electron beam through such agrid is lO-odd to 20-odd percent and the temperature of the gridelements rises up to I00 C. to C. Consequently this type of gridstructure encounters the same problems as in the Chromatron (RegisteredTrademark) type color cathode-ray tube.

In addition to the sag of the grid elements, nonuniformity in thetension applied to the grid elements raises another problem in such agrid structure as mentioned above. Even slight nonuniformity in thetension causes the grid elements to twist and the space between adjacentgrid elements becomes wider in a direction normal to the incidentdirection of the electron beam, although the pitch of the grid elementsremains unchanged. As a result of this, there is the possibility thatthe electron beam strikes on a phosphor strip other than a predeterminedone, especially a phosphor strip adjacent the predetermined one to causeunnecessary color emission.

Therefore, the nonuniforrnity in the tension applied to the gridelements should be avoided.

Accordingly, it is an object of this invention to provide a cathode-raytube of the single gun, plural beam type which is free of theabove-mentioned disadvantages characteristics of tubes of that type aspreviously proposed and which is particularly suited to serve as a colorpicture tube for producing color pictures of high resolution andbrightness.

Another object of this invention is to provide a cathode-ray tubeparticularly a color picture tube which is of the single gun, pluralbeam type and can be relatively easily manufactured even whenminiaturized to a considerable degree.

A further object of this invention is to provide a cathode-ray tube inwhich a grid structure is provided such that the grid elements arealways subjected to a predetermined tension and do not sag duringoperation though heated by electron beams.

Yet another object of this invention is to provide a grid structure forshadow mask type color cathode-ray tubes in which the grid elementsheated by electron beams do not sag during operation to thereby insureuniformity in the spacing between adjacent grid elements and henceprevent unnecessary bombardment of the phosphorus strips by the electronbeam.

A still further object of this invention is to provide the cathode-raytube with a grid structure which is constructed such that the gridelements are protected from shocks applied from the outside and causedby electron beam bombardment.

The above and further objects, features and advantages of the presentinvention will appear from the following detailed description of apreferred embodiment of the invention which is to be read in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a diagrammatic view illustrating the optical equivalent of asingle gun, plural beam system in which the beams are converged tosubstantially the optical center of an electrostatic focusing lens;

FIG. 2 is a plan view showing one example of a grid structure for colorcathode-ray tubes produced according to this invention; and

FIG. 3 is a side view of the grid structure illustrated in FIG. 2.

Referring now to the figures there is illustrated in FIG. I the opticalequivalent of a cathode-ray tube having a single electron gun thatgenerates a plurality of electron beams that are converged tosubstantially the optical center of a focusing lens. The single electrongun A includes equivalent beam generating sources K,, K, and K, whichare located on a straight line in a plane substantially perpendicular tothe axis of the electron gun and spaced apart from each other by adistance d,. These beam generating sources K,, K,, and K, have beenconverged to an area of minimum cross section by means not illustratedsuch that the area of minimum cross section of each of the beams is atthe position designated K,, K, and K, The beam generating sources emitthree electron beams 3,, B, and 8,, respectively, which are refracted bymeans of a common auxiliary lens L so as to be converged substantiallyat the optical center of a main focusing lens L. Thus, the three 8,, B,and B, are made to cross each other at substantially the optical centerof the main focusing lens L and then to emerge from the focusing lens Lin divergent directions. Subsequently the beams B, and B, which divergefrom the optical axis and from the beam B, lying on such axis aredeflected toward the center beam B, by means of convergence deflectorsF, and F, provided between the electron receiving screen S and the mainlens L and spaced from the latter by a distance 1 so that the three beamspots 8,, B and B, on the screen are converged or superimposed on eachother.

With the arrangements shown in FIG. I therefor very small beam spots canbe obtained since all three beams 13,, B, and B, pass through the centerof the main focusing lens L and thus the focused beam spots areprevented from being blurred due to various spherical aberrations.Consequently a picture with a high resolution can be produced.Furthermore, utilization of the deflectors F, and F advantageouslyfacilitates the dynamic convergence correction with respect to the threebeams.

It is to be understood that although FIG. 1 illustrates the beamgenerating sources K,, K, and K, as lying in a straight line and theelectron beams being refracted by means of a common auxiliary lens L soas to be converged substantially at the optical center of the mainfocusing lens L the same thing can be accomplished by arranging the beamgenerating sources I(,, K, and K, on a arcuate surface. In this respectFIG. I is merely illustrative and not in any way meant to limit thescope of this invention.

As explained in copending Pat. application Ser. No. 790,350, filed Jan.l0, I969, entitled GRID STRUCTURE FOR COLOR PICTURE TUBES and assignedto the same assignee as this patent application, a grid structure ispositioned adjacent the electron receiving screen and therefor betweenthe electron gun and the electron receiving screen. The construction ofthis grid structure is illustrated in FIGS. 2 and 3.

As clearly shown in the figures, the grid structure of this inventioncomprises a frame of a predetermined configuration which consists of barsupports 4 and 4' and a pair of substantially C-shaped resilientsupports 5 and 5 supporting the bar supports 4 and 4' at locationsspaced inwardly from the ends thereof, and more particularly at or inthe vicinity of the Bessel points 8,, B, and B,,', B, thereof, and aplurality of ribbon-shaped grid elements of, for example, stainlesssteel are stretched between the bar supports 4 and 4' at a predeterminedpitch under predetermined distribution of tension. Reference numeral 7indicates generally the grid structure.

The bar supports 4 and 4' may be formed of a metal such as iron,stainless steel or the like and in the illustrated example the barsupports 4 and 4 are square in cross section and are bent to conform tothe panel to which the grid structure will be attached. The resilientsupports 5 and 5' may be formed of a metal such as iron, stainless steelor the like and are substan tially C-shaped so as not to disturb theirradiation of the phosphor screen by the electron beam emitted from theelectron gun of a cathode-ray tube. It is a matter of course that thesupports 5 and 5' may be configured at will so long as they do notdisturb the electron beam directed to the fluorescent screen of thecathode-ray tube. The grid elements 6 may also be formed of a metal suchas iron, stainless steel or the like.

With such an arrangement, since the pair of bar supports 4 and 4'constituting one portion of the frame are jointed to the resilientsupports 5 and 5' as a unitary structure at or in the vicinity of theBessel points 8, B, and B and B,,', the bar supports 4 and 4' may beregarded as a rigid body with respect to the load caused by the tensionof the grid elements. The term Bessel points," as used herein, has itsaccepted meaning and refers to those points along each of bar supports 4and 4' spaced inwardly from the ends of the bar supports by a distanceequal to about 0.2232 X the length of the bar support so that, when thelatter is loaded substantially equally along its length, as by thetension in grid elements 6, and supported at the Bessel points, as bythe supports 5 and 5', the deflections of each of bar supports 4 and 4'at the ends thereof will be equal to the deflection at the center andthe deflections at the ends and center will be minimized. Accordingly,when the grid elements 6 that are stretched between the bar supports 4and 4' uniformly at a predetermined tension expand by heat resultingfrom the electron beam bombardment thereon, the bar supports 4 and 4'are pulled outwards by the resilient supports 5 and 5' in a parallelrelationship by a distance corresponding to the length of the gridelements which have been extended by the thermal expansion.Consequently, although the ab solute value of the tension is differentfrom the initial one, the initial distribution of the tension over theentire grid elements remains unchanged.

The foregoing description has been made in connection with a gridstructure in which the grid elements are of substantially the samelength at the both end portions and central portion of the bar supportsand hence they are expanded substantially equally due to thermalexpansion. According to our experiments on a grid structure in which thebar supports of square cross section were made of stainless steel andhad a size of about It) mm. XIO mm. X240 mm. and 400 grid elements 0.5mm. wide, 0.I mm. thick and about I80 mm. long (the length of the gridelements on the end portions of the bar supports were I75 mm. and thatof the elements of the central portion: 185 mm.) were stretched betweenthe bar supports at a tension of about 350 g. for each grid element, ithas been ascertained that although the grid elements were heated byelectron beams and extended due to thermal expansion during operation,accidents such as vibration of the grid elements due to nonuniformity ofthe tension or color contamination due to irregularity of the spacebetween adjacent grid elements were not caused. Further, it has beenfound that the deviation from the initial distribution of the tension ofthe grid elements caused by the thennal expansion thereof resulting fromthe collision of the electron beam therewith were compensated for by thestretch or shrinkage of the grid elements or slight restoring force ofthe bar supports.

In addition, it has also been found that if the deviation of the lengthof the grid elements is in a range of percent relative to its meanvalue, the length of the grid elements extended by the thermal expansionis extremely short and the initial distribution of the tension of thegrid elements is maintained during operation by the stretch andshrinkage of the grid elements or by compensation due to the restoringforce of the bar supports.

The grid structure is assembled with the panel of a cathoderay tube inthe following manner. Resilient pieces of a predetermined shape aresecured to the resilient supports 5 and 5' and the bar support, forexample, 4, each resilient piece having bored therethrough an apertureat the free end. It is preferred that an elongated hole extending in thedirection of the grid elements be formed in at least one of theresilient pieces secured to the resilient supports. Projections areprovided on the sides of the panel on the inside thereof and theprojections are inserted into the apertures of the resilient pieces inassembling the grid structure with the panel. In this case the resilientpieces and the projections of the panel may be four respectively.

In the aberration of the cathode-ray tube of the present invention,appropriate voltages are applied to the grids of the electron gun. Inthis manner the beams 8,, B, and B, emanat ing from the cathodes K,, K,and K, are made to cross each other substantially at the optical centerof the main focusing lens L. The beam: B, and B, emerge from the mainfocusing lens L along divergent paths. These three beams are acted uponby the convergence deflectors F and F, provided between the electronreceiving screen S and the main lens L and spaced from the latter by adistance so that the three beam spots 8,, B, and B, are converged orsuperimposed on each other. A color screen 5 comprised of sets of red,green and blue phosphorous strips has positioned before it the aperturegrill A of the present invention. The three beams 8,, B and B, are madeto cross each other at the position of the aperture grill A, and thus tolaiid on the corresponding phosphorous strips.

In the foregoing description the electron gun embodying this inventionhas been described as being applied specifically to colored picturetubes in which a single gun is employed to produce three electron beamswhich are intensity modulated with the usual red, green, and blue colorsignals. However, it is obvious that an electron gun in accordance withthis invention can be used in any other cathode-ray tube requiring aplurality of beams which are to be focused at a common spot or atseparated spots on an electron receiving screen.

Although illustrative embodiments of electron guns according to thisinvention have been described in detail herein with reference to theaccompanying drawings, it is to be understood that the invention is notlimited to those precise embodiments and that various changes andmodifications may be made therein by one skilled in the art withoutdeparting from the scope or spirit of the invention as defined in theappended claims.

What we drum is:

I. A cathode-ray tube comprising beam producing means for producing aplurality of electron beams, a screen having arrays of different colorphosphors and being positioned to have said beams impinge on respectivecolor phosphors of said arrays for exciting the same, means for causingsaid beams to intersect at a location in the tube between said beamproducing means and said screen, whereby said beams diverge with respectto each other in traveling toward said screen from said location,focusing lens means for focusing all of said beams on said screen, saidfocusing lens means having an equivalent optical center and beingpositioned to dispose said optical center substantially at said locationwhere the beams intersect, convergence deflection means positionedbetween said focusing lens means and said screen and operating on atleast certain of said beams diverging with respect to each other tocause the beams to again intersect each other in a plane in advance ofsaid screen, and a grid structure positioned in said plane in advance ofsaid screen and having parallel slits through which said beams can passfor impingement on the respective phosphors of said arrays.

2. A cathode-ray tube according to claim 1, in which said grid structureincludes a pair of opposed, spaced-apart sup port bars, a set ofsubstantially parallel, spaced-apart elongated elements extendingbetween said support bars and defining said slits between said elements,and a pair of braces extending between said support bars and beingstressed in compression while said elements are stressed in tension sothat, when said elements expand in response to heating thereof, saidbraces maintain said elements under tension.

Disclaimer 3,596,126.Swsumu Yoshz'da and Akz'o Ohgoshi, Tokyo, SemiMz'yaolca, KamigaWa-ken, and Yoshz'ham Katagiri, Tokyo, J a an. OATHODERAY TUBE WITH PARALLEL SLIT GRI TRUCTURE ADJ A- CENT COLOR DISPLAYSCREEN. Patent dated July 27, 1971. Disclaimer filed Apr. 7, 1972, bythe assignee, Sony Corporation. Hereby disclaims the portion of the termof the patent subsequent to June 3, 1986.

[Oficial Gazette May 9, 1.972.]

1. A cathode-ray tube comprising beam producing means for producing aplurality of electron beams, a screen having arrays of different colorphosphors and being positioned to have said beams impinge on respectivecolor phosphors of said arrays for exciting the same, means for causingsaid beams to intersect at a location in the tube between said beamproducing means and said screen, whereby said beams diverge with respectto each other in traveling toward said screen from said location,focusing lens means for focusing all of said beams on said screen, saidfocusing lens means having an equivalent optical center and beingpositioned to dispose said optical center substantially at said locationwhere the beams intersect, convergence deflection means positionedbetween said focusing lens means and said screen and operating on atleast certain of said beams diverging with respect to each other tocause the beams to again intersect each other in a plane in advance ofsaid screen, and a grid structure positioned in said plane in advance ofsaid screen and having parallel slits through which said beams can passfor impingement on the respective phosphors of said arrays.
 2. Acathode-ray tube according to claim 1, in which said grid structureincludes a pair of opposed, spaced-apart support bars, a set ofsubstantially parallel, spaced-apart elongated elements extendingbetween said support bars and defining said slits between said elements,and a pair of braces extending between said support bars and beingstressed in compression while said elements are stressed in tension sothat, when said elements expand in response to heating thereof, saidbraces maintain said elements under tension.